A known technology described, for instance, in JP-A No. 183610/2004, uses electric motors to drive an intake valve and exhaust valve for each cylinder.
However, if the above technology, which uses electric motors to drive the intake valve and exhaust valve for each cylinder, is employed, it is anticipated that, for example, the electric motors or sensors for detecting the rotational position of the electric motors may become faulty. If an internal combustion engine is continuously operated by using normal cylinders only, the explosion stroke becomes irregular, thereby changing the rotary torque. This causes deteriorated driveability or makes it difficult to continue operating the internal combustion engine.
The present invention has been made to solve the above problem. It is an object of the present invention to carry out the explosion stroke regularly and prevent driveability from deteriorating in a situation where the internal combustion engine is not operated with all cylinders.